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Fire Protection Technical Information

The information below provides a brief background to some of the technical aspects relating to intumescents and fire protection including:

  • Fire Types
  • The behaviour of structures in fire

Cellulosic Fire

Cellulosic fires are fuelled by combustibles such as wood, paper, textiles, etc. The cellulosic standard fire curve reaches 500°C [932°F] within 5 minutes and rises to in excess of 1100°C [2012°F] over time.

Fire Types

Real fires can have an infinite number of variations with respect to growth phase, peak temperature and duration. However, to allow for benchmarking between fire protection products, the industry has adopted standard fire curves for different types of fires.

The standard fire curves aim to replicate the severe exposure conditions of a fire such as those that typically occur following flashover within a compartment.

Section Factor Concept

The ‘section factor’ is a very important concept when using passive fire protection on structural steelwork. The section factor (Hp/A) is the ratio of the fire exposed perimeter to the cross sectional area of the steel.

Essentially it is a measure of how quickly the steel section will heat in a fire, and therefore how much fire protection is required.

Section Factors: Rates of Heating

A low section factor equates to a stocky section which when unprotected will take longer to heat to a set critical temperature than a relatively slender section of high section factor. The inherent fire resistance of a stocky section therefore requires this section to have less fire protection to achieve the same fire resistance rating.

Typically beams with a concrete slab on top are exposed on 3 sides, while columns are exposed on all 4 sides. The covering of one side can have a large reduction in the amount of fire protection required.

  • Establishing a thickness of intumescent paint
  • Fire resistance ratings
  • Section factor concept
  • Limiting temperature concept
  • Mechanisms of intumescents

Hydrocarbon and Jet Fires

Hydrocarbon fires, or pool fires, are fuelled by oil and gas and have a very rapid heat rise to 1000°C [1832°F] within 5 minutes and rises to 1100°C [2012°F] shortly thereafter. Hydrocarbon fires are also extremely turbulent as the fire entrains oxygen to maintain combustion. Jet fires are a particular group of hydrocarbon fuelled fires expelled from an orifice under pressures of 2 bar or greater.

The Behaviour of Structures in Fire

The response of a steel structure in a fire can be influenced by the maximum temperature attained, the degree to which it is loaded, the degree of support and restraint (geometry and design) and the temperature dependent mechanical properties of the steel.

The term ‘Fire Resistance Rating’ is associated with the ability of a building element to perform its function as a barrier or structural component for a specified time during the course of a fire. The rating is typically specified in accordance with structural design guidance documents and standards in combination with a critical core temperature. The most common periods are 60 minutes, 90 minutes or 120 minutes.

Intumescent Coatings

Intumescent coatings react to heat by swelling in a controlled manner to many times their original thickness to produce a carbonaceous char which acts as an insulating layer to product the steel section to which it is applied.

Intumescence is a complex process in which chemical reactions take place to convert the coating to a viscous liquid. At the same time, gases are produced and trapped within the liquid. This causes the swelling and formation of the insulating char.

The intumescent mechanism and subsequent char formation absorbs heat from the fire helping to keep the temperature of the steel below its limiting temperature and to provide the required period of structural fire-resistance.